JP2006076442A - Pneumatic tire for racing cart - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a tire 2 for a racing cart capable of being embodied at low cost and excellent in the cornering performance. <P>SOLUTION: The tire 2 is equipped with a tread 4, side walls 6, beads 8, a carcass 10, and an inner liner 12. The tensile stress in the rubber of the tread 4 at 300% elongation is 1.5-5.0 kPa, including the limits. The carcass 10 is composed of a first carcass ply 20 and a second carcass ply 22. The absolute value of the angle of the cords in the carcass plies 20 and 22 to the circumferential direction is 25-38°, including the limits. The JIS-A hardness of the topping rubber of the carcass plies 20 and 22 is 50-80, including the limits. The bead 8 consists of a core 16 and apex 18. The dynamic storage modulus of elasticity E' of the apex 18 measured under the conditions of a temperature of 70°C, a frequency of 10 Hz, and an amplitude of 2% is no less than 100 MPa. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a pneumatic tire mounted on a racing cart.

  The racing cart has a single-seat vehicle body, and a tire having an outer diameter of 350 mm or less and an aspect ratio of 0.5 or less is attached to the vehicle body. In the cart race, lap times are competed. Since this racing cart has a low center of gravity and is lightweight, the turning speed in car racing is fast. The cart may be single-wheeled when turning. A very large lateral force is applied to racing cart tires. In order to shorten the lap time, racing cart tires are required to have high lateral rigidity and excellent resilience.

  Tires are roughly classified into bias tires and radial tires. The tire for the racing cart is regulated by the regulation to be a bias tire. On the other hand, since car racing has a mission to expand the bottom layer of motor sports, tires for racing carts need to be obtained at low cost. The degree of design freedom for racing cart tires is not very high.

Various devices relating to the material of the carcass cord intended to improve various performances of the tire have been proposed. For example, JP 2003-54215 A and JP 2003-237308 A disclose tires using a carcass cord made of polyethylene naphthalate fiber.
JP 2003-54215 A JP 2003-237308 A

  When the height of the turn-up end of the carcass ply is set to be large, a racing cart tire having high lateral rigidity can be obtained. This carcass ply increases not only the lateral stiffness but also the longitudinal stiffness. A tire having a large longitudinal rigidity is inferior in road surface followability. This tire may cause deterioration of lap time.

  If a reinforcing layer is provided around the bead or on the sidewall, a racing cart tire having high lateral rigidity can be obtained. This reinforcing layer causes an increase in the number of parts and an associated increase in manufacturing cost. And the manufacturing process of the tire provided with the reinforcement layer is complicated. Furthermore, the reinforcing layer is contrary to the demand for weight reduction of the tire.

  An object of the present invention is to provide a racing cart tire that is obtained at low cost and has excellent turning performance.

  The racing cart tire according to the present invention has a tread whose outer surface forms a tread surface, a pair of sidewalls extending substantially inward in the radial direction from the end of the tread, and further inward in the radial direction from the sidewalls. A pair of extending beads and a carcass spanned between the beads. The tensile stress at 300% elongation of the rubber of this tread is 1.5 kPa or more and 5.0 kPa or less. This carcass includes two carcass plies. The carcass ply includes a cord made of polyethylene naphthalate fiber and a topping rubber. The absolute value of the angle of the carcass cord with respect to the circumferential direction is 25 ° or more and 38 ° or less.

  Preferably, the JIS-A hardness of the topping rubber of the carcass ply is 50 or more and 80 or less.

  The bead includes a core and a tapered apex extending radially outward from the core. The dynamic storage elastic modulus E ′ of the Apex rubber measured under the conditions of a temperature of 70 ° C., a frequency of 10 Hz, and an amplitude of 2% is preferably 100 MPa or more.

  The present invention is suitable for a tire having an outer diameter of 350 mm or less.

  This racing cart tire achieves high lateral rigidity and excellent resilience due to the synergistic effect of the tread whose tensile stress when stretched at 300% is 1.5 kPa or more and 5.0 kPa or less and the carcass cord excellent in elasticity. Is done. This tire is excellent in turning performance.

  Hereinafter, the present invention will be described in detail based on preferred embodiments with appropriate reference to the drawings.

  FIG. 1 is a cross-sectional view showing a part of a racing cart tire 2 according to an embodiment of the present invention. In FIG. 1, the vertical direction is the radial direction of the tire 2, and the horizontal direction is the axial direction of the tire 2. The tire 2 has a substantially left-right symmetric shape centered on a one-dot chain line CL in FIG. This alternate long and short dash line CL represents the equator plane of the tire 2. The outer diameter of the tire 2 is 350 mm or less, particularly 300 mm or less. The tire 2 includes a tread 4, a sidewall 6, a bead 8, a carcass 10, and an inner liner 12. The tire 2 is a pneumatic tubeless tire.

  The tread 4 is made of a crosslinked rubber and has a circular arc shape protruding outward in the radial direction. The outer surface of the tread 4 constitutes a tread surface 14 that contacts the road surface. The tread surface 14 has no groove. The tire 2 is a so-called slick tire. The tread surface 14 may include a tread pattern including grooves, blocks, and the like.

  The sidewall 6 extends substantially inward in the radial direction from the end of the tread 4. The sidewall 6 is made of a crosslinked rubber. The sidewall 6 absorbs an impact from the road surface by bending. Further, the sidewall 6 prevents the carcass 10 from being damaged.

  The bead 8 extends from the sidewall 6 substantially inward in the radial direction. The bead 8 includes a core 16 and an apex 18 extending from the core 16 substantially outward in the radial direction. The core 16 has an annular shape and is composed of a plurality of non-stretchable wires (typically steel wires). The apex 18 has a tapered shape that tapers outward in the radial direction, and is made of a crosslinked rubber.

  The carcass 10 is bridged between the beads 8 on both sides so as to be along the inner surfaces of the tread 4, the sidewalls 6, and the beads 8. The carcass 10 includes a first carcass ply 20 and a second carcass ply 22. The first carcass ply 20 and the second carcass ply 22 are wound around the core 16 from the inner side to the outer side in the axial direction.

  The inner liner 12 is joined to the inner surface of the carcass 10. The inner liner 12 is made of a crosslinked rubber. The inner liner 12 is made of rubber having a low air permeability. The inner liner 12 serves to maintain the internal pressure of the tire 2.

  FIG. 2 is an enlarged cross-sectional view showing a part of the carcass 10 of the tire 2 of FIG. In FIG. 2, what is indicated by a double arrow A is the circumferential direction of the tire 2. The first carcass ply 20 includes a large number of cords 24 arranged in parallel and a topping rubber 26. The cord 24 is embedded in the topping rubber 26. All cords 24 are approximately the same diameter. The cord 24 is inclined with respect to the circumferential line L1. The absolute value of the angle of the cord 24 with respect to the circumferential direction is indicated by a double arrow α. The second carcass ply 22 includes a large number of cords 28 arranged in parallel and a topping rubber 30. The cord 28 is embedded in the topping rubber 30. All cords 28 are approximately the same diameter. The cord 28 is inclined with respect to the circumferential line L2. The absolute value of the angle of the cord 24 with respect to the circumferential direction is indicated by a double arrow β.

  The direction of inclination of the cord 24 of the first carcass ply 20 is opposite to the direction of inclination of the cord 28 of the second carcass ply 22. In other words, the direction of the cord 24 of the first carcass ply 20 and the direction of the cord 28 of the second carcass ply 22 intersect each other. The tire 2 is a so-called bias tire. The tire 2 is excellent in road surface followability.

  The angles α and β are not less than 25 ° (degree) and not more than 38 °. By setting the angles α and β to 25 ° or more, the longitudinal rigidity of the tire 2 is suppressed. The tire 2 is excellent in road surface followability. From the viewpoint of road surface followability, the angles α and β are more preferably 27 ° or more. By setting the angles α and β to 38 ° or less, an appropriate longitudinal rigidity can be obtained. The tire 2 is excellent in handling stability. In this respect, the angles α and β are more preferably 35 ° or less. The angles α and β are measured at the equatorial plane. For the measurement, a test piece cut out from the tire 2 is used.

  The cords 24 and 28 are made of polyethylene naphthalate fiber. Polyethylene naphthalate fiber has a high elastic modulus. By using the polyethylene naphthalate fiber, the tire 2 having high lateral rigidity and excellent resilience can be obtained. The tire 2 is excellent in turning performance.

  It is preferable that the cords 24 and 28 having a fineness of 500 dtex or more are used for the carcass 10. The carcass 10 suppresses deformation when a lateral force is applied to the tire 2. The tire 2 is excellent in turning performance. From the viewpoint of turning performance, the fineness of the cords 24 and 28 is more preferably 900 dtex or more. From the viewpoint of road surface followability, the fineness of the cords 24 and 28 is preferably 2500 dtex or less, and more preferably 2000 dtex or less.

  From the viewpoint of suppressing deformation when a lateral force is applied to the tire 2, the density of the cords 24 and 28 (the number per 5 cm) is preferably 30 ends or more, and more preferably 35 ends or more. From the viewpoint of road surface followability, the density of the cords 24 and 28 is preferably 70 ends or less, and more preferably 60 ends or less.

  From the viewpoint of suppressing deformation when a lateral force is applied to the tire 2, the product of the fineness (dtex) and the density (end) of the cords 24 and 28 is preferably 20000 or more, and more preferably 25000 or more. From the viewpoint of road surface followability, this product is preferably 120,000 or less, and more preferably 100,000 dtex or less.

  The cords 24 and 28 may be formed by twisting two or more fibers. In this case, the number of twists per 10 cm is preferably 25 times or more and 55 times or less. The carcass 10 may be composed of three or more carcass plies.

  The carcass 10 uses topping rubbers 26 and 30 having a hardness of 50 or more. The carcass 10 suppresses deformation when a lateral force is applied to the tire 2. The tire 2 is excellent in turning performance. From the viewpoint of turning performance, the hardness is more preferably 55 or more, and particularly preferably 60 or more. From the viewpoint of road surface followability, the hardness is preferably 80 or less, and more preferably 75 or less. The hardness is measured by a type A durometer in accordance with the provisions of “JIS K 6253”. For the measurement, a slab made of the same rubber composition as the rubber composition of the topping rubbers 26 and 30 is used. The thickness of the slab is 8 mm. A slab is obtained by holding the rubber composition in a mold having a temperature of 160 ° C. for 10 minutes.

For the tread 4 (see FIG. 1), rubber having a tensile stress of 1.5 kPa or more at 300% elongation is used. The tread 4 suppresses deformation when a lateral force is applied to the tire 2. Due to the synergistic effect of the tread 4 and the carcass 10 using polyethylene naphthalate fibers, the tire 2 exhibits excellent turning performance. From the viewpoint of turning performance, the tensile stress is more preferably 2.0 kPa or more, and particularly preferably 2.3 kPa or more. From the viewpoint of handling stability, the tensile stress is preferably 5.0 kPa or less, and more preferably 4.5 kPa or less. The tensile stress is measured under the conditions shown below in accordance with the provisions of “JIS-K 6251”.
Tensile tester: Trade name "Strograph T type" by Toyo Seiki Seisakusho
Test piece shape: Dumbbell No. 3 Tensile speed: 500 mm / min
This test piece is cut out from the tread 4. When it is difficult to cut out, a test piece is punched out from a slab made of the same rubber composition as that of the tread 4. A slab is obtained by holding the rubber composition in a mold having a temperature of 160 ° C. for 10 minutes.

  The apex 18 is made of rubber having a dynamic storage elastic modulus E ′ of 100 MPa or more. The apex 18 has extremely high hardness. When a lateral force is applied to the tire 2, a large reaction force is generated by the apex 18. The tire 2 has high lateral rigidity. The hardness of the apex 18 does not significantly affect the longitudinal rigidity of the tire 2. In the tire 2, the longitudinal rigidity is not excessive and the lateral rigidity is large. In the tire 2, road followability and resistance to lateral force are compatible at the time of turning. In the tire 2, excellent turning performance is exhibited. From the viewpoint of turning performance, the storage elastic modulus E ′ is more preferably 105 MPa or more, and particularly preferably 110 MPa or more. The storage elastic modulus E ′ is usually 150 MPa or less.

The storage elastic modulus E ′ is measured by a viscoelastic spectrometer (“VES / F-3 type” manufactured by Iwamoto Seisakusho Co., Ltd.) under the conditions shown below in accordance with the provisions of “JIS-K 6394”.
Initial strain: 10%
Amplitude: 2%
Frequency: 10Hz
Deformation mode: Tensile Start temperature: -100 ° C
End temperature: 100 ° C
Temperature increase rate: 3 ° C / min
Measurement temperature: 70 ° C

  The test piece used for the measurement by a viscoelastic spectrometer is plate shape, the length is 45 mm, the width is 4 mm, and the thickness is 2 mm. Measurement is performed by chucking both ends of the test piece. The length of the displacement part of the test piece is 30 mm. This test piece is cut out from the apex 18. When it is difficult to cut out, a test piece is punched out from a slab made of the same rubber composition as the apex 18 rubber composition. A slab is obtained by holding the rubber composition in a mold having a temperature of 160 ° C. for 10 minutes.

As a method of obtaining a high hardness Apex 18,
(1) Increase the compounding amount of the crosslinking agent in the rubber composition (2) Increase the compounding amount of the reinforcing agent in the rubber composition (3) Use a special base rubber for the rubber composition (4) Rubber composition For example, a resin may be added to the product.

  In FIG. 1, what is indicated by a double arrow H1 is the height of the tire 2, and what is indicated by a double arrow H2 is the height of the end 32 of the carcass 10. In light of suppression of the longitudinal rigidity of the tire 2, the ratio (H2 / H1) is preferably equal to or less than 0.90, and more preferably equal to or less than 0.85. In the tire 2, the cords 24 and 28 made of polyethylene naphthalate fiber are used for the carcass 10, and rubber having a large tensile stress is used for the tread 4, so that the ratio (H2 / H1) is small. High lateral stiffness has been achieved. The ratio (H2 / H1) is usually 0.3 or more.

  In the present invention, the outer diameter, the height H1, and the height H2 of the tire 2 are measured in a state where the tire 2 is incorporated in a regular rim and the tire 2 is filled with air so as to have a regular internal pressure. At the time of measurement, no load is applied to the tire 2. In the present specification, the normal rim means a rim defined in a standard on which the tire 2 depends. “Standard rim” in the JATMA standard, “Design Rim” in the TRA standard, and “Measuring Rim” in the ETRTO standard are regular rims. In the present specification, the normal internal pressure means an internal pressure defined in a standard on which the tire 2 relies. “Maximum air pressure” in JATMA standard, “Maximum value” published in “TIRE LOAD LIMITS AT VARIOUS COLD INFLATION PRESSURES” in TRA standard, and “INFLATION PRESSURE” in ETRTO standard are normal internal pressures.

  In the tire 2, high lateral rigidity is achieved by using the cords 24 and 28 made of polyethylene naphthalate fiber for the carcass 10 and using rubber having a large tensile stress for the tread 4. Therefore, it is not necessary to use another member (for example, a reinforcing layer) for the purpose of improving the lateral rigidity. The manufacturing process of the tire 2 is simple. The tire 2 can be obtained at a low cost. Of course, other members may be used in an auxiliary manner.

  Hereinafter, the effects of the present invention will be clarified by examples. However, the present invention should not be construed in a limited manner based on the description of the examples.

[Example 1]
A tire having the structure shown in FIGS. 1 and 2 was obtained. This tire includes a first carcass ply having an angle α of 30 ° and a second carcass ply having an angle β of 30 °. The JIS-A hardness of the carcass ply topping rubber is 70. A cord made of polyethylene naphthalate fiber is used for the carcass ply. The fineness of the cord is 1670 dtex. The cord density is 50 ends. For the tread, rubber having a tensile stress of 2.3 kPa at 300% elongation is used. In the apex, rubber having a dynamic storage elastic modulus E ′ of 50 MPa is used. The tire has a size of “11 × 7.10-5”, an outer diameter of 280 mm, and a ground contact width of 160 mm.

[Comparative Examples 1 and 2 and Example 3]
Tires of Comparative Examples 1 and 2 and Example 3 were obtained in the same manner as in Example 1 except that rubber having a tensile stress shown in Table 1 below was used for the tread.

[Example 2]
A tire of Example 2 was obtained in the same manner as Example 1 except that rubber having a dynamic storage elastic modulus E ′ shown in Table 1 below was used for the apex.

[Comparative Examples 3 and 5]
Tires of Comparative Examples 3 and 5 were obtained in the same manner as in Example 1 except that the material of the carcass cord was changed as shown in Table 1 below. The fineness of the carcass cords of Comparative Examples 3 and 5 is 1670 dtex.

[Comparative Example 4]
A tire of Comparative Example 4 was obtained in the same manner as in Example 1 except that rubber having tensile stress shown in Table 1 below was used for the tread and the material of the carcass cord was changed as shown in Table 1 below. The fineness of the carcass cord of this tire is 1670 dtex.

[Evaluation]
A “8.0 × 5” rim was incorporated into the tire, and the internal pressure of the tire was set to 80 kPa. This rim was attached to the racing cart as a rear wheel, and the cart course with a total length of 716 m made 10 laps. The lap times on the third and sixth laps at this time were measured. The results are shown in Table 1 below.

  As shown in Table 1, the tires of the examples have a short lap time, and the difference between the lap time on the third lap and the lap time on the sixth lap is small. From this evaluation result, the superiority of the present invention is clear.

  The present invention can be applied not only to a tire for a rear wheel of a racing cart but also to a tire for a front wheel.

FIG. 1 is a cross-sectional view showing a part of a racing cart tire according to an embodiment of the present invention. FIG. 2 is an enlarged cross-sectional view showing a part of the carcass of the tire of FIG.

Explanation of symbols

2 ... Tracing tire 4 ... Tread 6 ... Side wall 8 ... Bead 10 ... Carcass 12 ... Inner liner 14 ... Tread surface 16 ... Core 18 ... Apex 20 ... first carcass ply 22 ... second carcass ply 24, 28 ... cord 26, 30 ... topping rubber

Claims (4)

A tread whose outer surface forms a tread surface, a pair of sidewalls extending substantially inward in the radial direction from the end of the tread, a pair of beads extending further inward in the radial direction from the sidewalls, and between the two beads With a carcass
The tread rubber has a tensile stress at 300% elongation of 1.5 kPa to 5.0 kPa,
This carcass includes two carcass plies including a cord made of polyethylene naphthalate fiber and a topping rubber,
A pneumatic tire for a racing cart in which an absolute value of an angle of the carcass cord with respect to a circumferential direction is 25 ° or more and 38 ° or less.   The pneumatic tire according to claim 1, wherein the topping rubber of the carcass ply has a JIS-A hardness of 50 to 80. The bead includes a core and a tapered apex extending substantially outward in the radial direction from the core;
The pneumatic storage according to claim 1 or 2, wherein the dynamic storage elastic modulus E 'of the Apex rubber measured at 70 ° C, a frequency of 10Hz, and an amplitude of 2% is 100 MPa or more. tire.   The pneumatic tire according to any one of claims 1 to 3, wherein the outer diameter is 350 mm or less.

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